Bitumen froth typically results from a primary separation of a slurry that includes water and oil sands ore. Bitumen froth treatment operations include a secondary separation, in which solvent (also referred to as diluent in some cases) is added to the bitumen froth for separation into a diluted bitumen stream and a tailings stream. The solvent can include paraffinic hydrocarbons (e.g., alkanes at varying ratios of linear alkanes and branched alkanes) for paraffinic froth treatment, but other froth treatment processes can use naphthenic diluent or other compounds. The solvent diluted bitumen (also called “dilbit”) can have a high solvent content (e.g., 65% solvent by weight).
In a paraffinic bitumen froth treatment process, for example, bitumen froth derived from oil sands ore is combined with paraffinic solvent and then processed in a froth settling vessel in which the diluted bitumen overflow is separated from a bottoms fraction that includes bitumen asphaltenes, water, solvent and mineral solids as well as residual amounts of bitumen maltenes.
Before the diluted bitumen overflow can have the proper specifications for pipeline transportation, storage facilities or further processing in downstream processing facilities, solvent must be removed from the dilbit in a solvent recovery unit (SRU) to produce a bitumen stream and a recovered solvent stream. Conventional SRUs include stages for pre-heating the dilbit and separating the solvent from the dilbit. The bitumen product from the SRU has a very low solvent content (<5,000 ppm by weight) and the recovered solvent stream is recycled for use in the froth settling vessel.
One known approach for an SRU, such as disclosed in Canadian Patent No. 2,733,332, is to use one or more heat exchanger(s) to preheat the dilbit before solvent recovery. Hot downstream fluids from the final processing steps in the SRU, such as hot bitumen, can be used as heating media for this preheating.